The present invention relates to a support assembly for a rotating shaft and, more particularly, to a support assembly for a rotating shaft on which is mounted the grinding table of a bowl mill operable to pulverize materials such as fossil fuel materials including coal.
It is known that a range of materials such as fossil fuels including, for example, coal, foodstuffs, and agricultural products, may be pulverized in a pulverizing operation performed by a bowl mill. A bowl mill, in one typical configuration, includes a separator body and a grinding table. The grinding table is supported on the top axial end of a shaft for rotation within the separator body. Such a bowl mill also includes a plurality of grinding rolls supported within the separator body, each grinding roll being operable to exert a grinding force on the material to be pulverized which is disposed on the grinding table for effecting the pulverization thereof.
During the grinding operation, a gear drive motor drivingly rotates the grinding table via a worm screw meshingly coupled with a driven gear fixedly coaxially mounted to the shaft. The grinding table cooperates with the grinding rolls to pulverize the material to be pulverized which, for illustrative purposes, will be considered to be coal. During this grinding process, the grinding table is subjected to radial and axial loading as coal particles of differing sizes and hardness are subjected to compressive action between the grinding rolls and the grinding table. Typically, the grinding rolls operate within a predetermined range of acceptable resistance force exerted on the grinding roll by the coal engaged between the grinding roll and the grinding table. If the acceptable resistance force is exceeded due to, for example, an encounter with a coal particle of relatively high hardness and of greater than a minimum size, then the is permitted to move out of grinding contact by, for example, overcoming the resilient bias of a spring biasing element acting on a journal supporting the grinding roll.
However, within the range of operation of the grinding rolls below those resistance forces which will cause a tripping out of a grinding roll, there is often an operating condition in which the grinding table is loaded in a manner which imposes radial forces on the shaft supporting the grinding table of the type which urge the shaft out of its axially centered--i.e., vertical-disposition. It can be appreciated, for example, that a loading may be transiently imposed on the grinding table at a radial spacing from the grinding table axis if a coal particle of a certain size and hardness is compressed between a grinding roll and the grinding table. Due to the fixed mounting of the grinding table on the top of the shaft, this offset radial loading is transmitted directly by the grinding table onto the shaft. It can also be appreciated that foreign matter such as tramp iron may be engaged between the grinding table and a grinding roll and this occurrence may cause offset radial loading of the grinding table and consequent radial displacement influences on the shaft.
Axial loading of the shaft is imposed by each compressive engagement of coal particles (or foreign matter) by the grinding table and the grinding rolls. Accordingly, it can be appreciated that the shaft is subjected, at some frequency, to simultaneous radial and axial loading and this operational reality presents a not insignificant challenge in providing effective and reliable rotational support of the shaft.
It has been proposed to provide a bowl mill with a combination of a thrust bearing arrangement and a bushing arrangement to handle the loading on the shaft supporting the grinding table and U.S. Pat. No. 2,079,155 to Crites is noted as representative of such a proposal. As disclosed in that patent, a bowl mill includes a shaft 19 supporting a bowl B and projecting freely downwardly through a sleeve 25. A hub 6 of the bowl B is journaled in a bearing sleeve or bushing 26 mounted in a bearing 5 which itself is mounted in a base plate 1 resting upon concrete pedestals. A lower end of a skirt 27 of the hub 6 is supported on an anti-friction thrust bearing 31. While the shaft rotational support arrangement disclosed in this patent may be adequate to handle the shaft loading situations outlined hereinbefore, it is still desirable to further optimize a shaft rotational support arrangement for a shaft of a bowl mill.